EN
Distribution pattern of δ¹³C values of plateau plants and their responses to environment along altitudinal gradients were investigated. In the growing season of 2003 (June– August), stable carbon isotope ratios (δ¹³C) of 174 plant samples belonging to 89 species of 20 families and 58 genera along the gradient 2800– 4400 m (above sea level) was studied in six sites on the east edge of Qinghai-Tibet Plateau. The results indicated that the range of δ¹³C values of plants is narrow from –30.2‰ to –25.2‰, which means that none of the species examined belonged to C₄ photosynthetic pathway and all of these species performed C₃ photosynthetic pathway. The average δ¹³C values of plants at 6 sites were positively correlated to altitude (r = 0.974, P <0.01). The results revealed that site-averaged δ¹³C values were negatively correlated with temperature (r = 0.907, P <0.05) as well as CO₂ partial pressure (r = 0.940, P <0.01). The combination of these two factors account for 80% of the variation of δ¹³C values (r² = 0.859, P <0.01). Varying precipitation with increasing altitude does not affect the plant δ¹³C values (r = 0.469, P> 0.05) as well as the sunlight duration(r = 0.630, P> 0.05).